15 



MOVEMENTS OF CURVATURE 



A still more striking instance of the same mechanism is afforded by 

 the ripe sporangium of Pilobolus crystallinus, which, according to Coemans, 

 may be thrown to a height of 105 centimetres. [Relatively to size, this is 

 higher than a man can throw a cricket-ball, even neglecting the air-resistance 



which, relatively to the masses, is several 

 hundred times greater in the case of the 

 sporangium. This energetic movement is 

 produced by the gradual swelling of the 

 basal membranous wall, which loosens the 

 union between the sporangium and the 

 swollen apex of the sporangiophore. The 

 latter then ruptures at the apex and the 

 jet of escaping liquid throws the sporan- 

 gium away J . The beginnings of this special 

 mechanism are seen in Mttcor, where the apex 

 of the sporangiophore (columella) bulges 

 into the sporangium and causes the rupture 

 of the brittle sporangial wall. The spores of 

 Empusa miiscae and of various Basidio- 

 mycetes are jerked away in a similar fashion 

 by pressures created by turgidity. Sper- 

 matozoa and zoospores when not ejected by 

 the dehiscence of the antheridium or zoo- 

 sporangium make their own way out through 

 the point of rupture, and the large zoospores 

 of Vaucheria may be nipped in two during 

 their exit from the narrow opening of the 

 zoosporangium 2 .] 



The hygroscopic movements of dead organs are often of great use 3 . 

 Thus the fact that many dry fruits and anthers open in dry air but close 

 when moistened ensures that the seeds or pollen-grains shall not be 

 dispersed during wet weather. Similarly the peristomes of many mosses 

 close the mouth of the capsule when moist but expand and allow 



FlG. 34 Sphaeria Scirpi (Pleospora 

 scirpicola) (after Pringsheim). A, unopened 

 ascus after the splitting of the cuticular mem- 

 brane. /?, the same with the spores all 

 escaped except one momentarily blocking 

 the apical opening. C, the same after all the 

 spores have escaped. 



1 Cf. de Bary, Morphologic u. Biologic der Pilze, 1884, PP- 77> 9! Z P f > Die Pilze> l8 9> 

 p. 81. 



1 On the escape of zoospores see de Bary, 1. c., p. 87 ; Falkenberg, in Schenck's Handbuch der 

 Botanik, 1882, Bd. n, p. 195 ; Strasburger, Wirkung des Lichtes und der Warme auf Schwarm- 

 sporen, 1878, p. 14; Walz, Bot. Ztg., 1874, p. 689; Rothert, in Cohn's Beitrage z. Biologic, 1892, 

 Bd. v, p. 344; Klebs, Bot. Ztg., 1891, p. 859; Goebel, Ann. du Jard. bot. de Buitenzorg, 1898, 

 Suppl. n, p. 65. 



3 Ludwig, Biologic d. Pflanzen, 1895, pp. 327, 344; Kerner, Pflanzenleben, 1891, Bd. II, p. 421 

 (Natural History of Plants, 1895, Vol. n, p. 447); Haberlandt, Physiolog. Pflanzenanatomie, 1896, 

 2. Aufl., pp. 469, 488 ; Hildebrand, Jahrb. f. wiss. Bot., 1873-4, Bd. IX, p. 245 ; Steinbrinck, Unters. 

 iib. d. anat. Ursachen des Aufspringens d. Friichte, 1873, Bot. Ztg., 1878, p. 561 ; Geovanozzi, Nuovo 

 giornale botanico italiano, 1901, T. vm, p. 207. 



